Process for the making of whitelead pigments



Feb. 26, 1935. N. c. CHRISTENSEN PROCESS FOR THE MAKING OF WHITE LEADPIGMENTS Original Filed Oct. 21, 1930 Can e12 y: 62161 5/? f/wBri/m CINYENTOR paten aatzs,193 I 1 992 19 V 1,992,1'91w- 1 l T PROCESS FORTHEMAKING F WHITE- 1 I "Niielsfl. Christensen, Salt Lake City, Utah 1Application October 21,1930, Serial No. 490,276 M i-c aims. (o1; 2s, 71)h v V J a a -This invention relates to processes'ifor theinanbonatesalts in less timegand ataflconsiderably ufacture of white leadp'igmentssuch aslead'carlower, cost than is possible: initheir manufacture bonateand basic leadjcarbonate'," orwhite-lead, f rorhrnj'ietallic lead, A 11j V from leadjchloride and lead chloride solutions; In the production ofwhite lead oarbonate prod- V i 5 Itlis especially j applicable andus'efulinfthe reucts by thisinvention anumber of"difierent steps .5

covery and making of such lead products from the areiinvolved, which 'nayiibeused alon or in' com 7 lead" chloride or lead-chloridesolutions-secured binationfdependingj upon thenature'ofltheifinal a in'th'e chloride brine leaching processes; described product i it .is idesired to: produce. a The primary inU. S. patents. f" stpsiorprooessesarewdescribedfirstland there-' 10 It is alsoiapplicable to themanufacture oflsuch' after various'combinationsi of these stepstoi-prolead products from Pb Clz and PbSOl fromv-other duce} the particular"lead moarbonate' products processesm .1 g i a 1-? 1* desired, 2 t Theobject ofthe inventionisjto produce these S),To:.produce the'substantiallyinomal -leadcarglead products directly from the treatmentof lead Ybonate, twoj differentf methodshm'aybe usedQde- 15. oresorother lead products by the brine leaching nending upon:thefitemperatureiof the solutions '5 a processes mentioned above ordirectly from lead -1 used in thetrea'tment iofthelead chloride; 'Both ichloride and lead sulphate lfromflotherfsources; fof thesemethodsinvolvethefltreatment of the without reducition of the-lead to metallicform lead, chloride with calcium carbonate (or other previous'to itsconversion tothese lead saltsand alkaline earth carbonate) :andwwater,eitherlin' lead pigfne'ntsQ; l ",j 1 A 1-; solution or as anemulsionwith water asbriefiy :afB'y this invention it is possible tomake whitedescribed in the following. i I x i lead carbonate pigniehtsiequal orsuperior: in iInexperiznenting-rwithlead chloride solutions, whitenesa'tinting strength andacovering -power lflhave found that thele'ad may. belprecipitated to the :white lead pigments produced from-me" fromitherhots'olution'orthe coldsolution bymeans' tallic lead by the corrosionprocesses nowin'com offlcalcimd carbonate. ::;The -:nature of ,1 the re-25 a mon use and which "also have a11-thedesirab1e 'actionand'thecharacter of theprecipitateuwill qualities as to oil"absorption,:vworkability," etc'., be entirely difierent intthe twocasesh liroma" possessed by. the products 'ofthe' olderprocess'es.cold'-water:so1ution of .leadt chloride the lead. is I By my inventionit is possible-to produce white j prec'ipitated asa lead-calcium chlorocarbonate I lead'pigments varying in basicity' from a substan-'asindicated in; thefollowing' chemical equation: 30

' tially normal carbonate, PbCOs, to thebasic'carv 1 '1 bonate,2PbCO3,Pb(OI-I)2. (purewhite lead) or i332m?t Q???iPP ?FPQQ -C 9 tc i" a'more' basic: product if desired. "I 'haveifound JThis reaotionfiscomplete aridfcquit'e rapid and thatthe qualitiesoftinting'strengthian'd hiding thyle dmay be'pracficfillly completelyprecipia J DOWer'increase with an increaseinbasicity of thetatedfromisolution byrthis method, The 1 1 1 35 l 7 l carbonate o p b cb beinglowest salt thus formedishowever not stable; in the in-the normallead carbonate PbCQsiand'increaspresence of water; but slowly:de mp li ia.

i gi p o r'bey nd h o n ryvbasi carbonate inglead carbonateand calciumchloride as indi; l 2Pb,C O3"Pb 2, dj j fii hest nt *eveh cated in, thefollowing chemical equation:

40 more basic products. v 1 v 1L, 1.1 :1";

a Contrary'to statements made in the literature Bb l 531 0 11 4i on hsubiectifit i p sib ebrn 'he methods" o The first reaction in which thelead chloride is this invention to secure a lead pigment of oprecipitated brooeeds quiterapidlyrbiit the-sec; 1 a quality as tintingre e w' r w 'k- 0nd reaction, which thexleadj is: completely con vability, oil absorption, eta; whichh'as'substanv r e l xcarbonatmpr'oeedsSlowly 45 ial y t D S the n fi at 'completelafterseveral hours agitationvvithlwater. 91 3, a d i hi ub t n ia equa in't e-Owingto the'li mited soiubiiityorP-bcu in co1d qualitiesrmentionfid,much of th White-lead water, it is nctveryreasibIe'tb carry out this ep-1 now sold as basic lead carbonate or White lead; rat bygdjssolvi'ng' tqe chldrid n to It is: not the object-of my: inventionvto' produce wa atpile timefland it istherefore desirable 1 the-whiteleadproductsn'ientioned'abovefor use; totreat the lead chloride'-i i1'solid iorm vvith water 'onlyaspaintpigments but also foi' useinmanu l'and calciurn carbonateto'oonvert the chloride to 1 faotu're of otherlead products "such' "as massicot; thecarbonate', 'Ifhisoperation'presents little dif litharge, red 1ead, 1ead 'peroxideetog', 'whiohmay-'fi ulty" if carriedout bygrinding-the;PbCl-'and Y 5i) vreadilybemadezldirectly fromqthese -lead"car Ca COs together in waterl Duringthfgfindilig fect of the brine concentration is shown in theaccompanyingcurves I and II." The coordinates of I are per cent NaClinsolution and grams Pb left in 100 .cc. of solution originallyapproximately saturated WithJPbCla' The coordinates of II are per centCaCl2 in solution and grams Pb left in 100 cc. of Solution originallyapproximately saturated with. PbClz. In running the tests to secure thepoints on these curves, slightly more than a chemicalequivalent of021003 to the PbCl -in solution was added-to the boiling solutionwhichwas then boiled'until any reaction between the CaCOz and PbClz waspractically completed. The solids were then filtered out and thesolution analyzed for Pb.

As will be-seen from thecurves; in' solutions carrying up to NaClsubstantially all of the.

lead is precipitated from solution as the basiclead-calcium-chloro-carbonate. In solutions carrying above 10% NaClthecompleteness of precipitation decreases slowly with increase in "NaClconcentration up to nearly 17%.% NaCl jand above this point the decreasein the completeness of precipitation varies almost directlyinpropor-,tion to the increase-in NaCl concentration until with. saturatedor-nearly saturated NaCl soluexcess. 'be slightly more basic.

lead chloridesoluticns as described hasapproxh.

mately the composition noted above; i. e., PbC12Pb|(OH)2.CaCO3, thoughthe exact composition will .vary slightly. from that givenaccording towhether the PbCl2 or CaCOa is in 'With an excess ofPbClz the salt mayFor example, if enough CaCO; is added to the boiling PbC12 solution toprecipitate the basic chlorocarbonate and PbClz is thereafter added. tothe-solution in which the precipitate is suspended, the PbClz willireactwith the CaCOs in the basic compound and drive off CO2 to form acompound containing more Pb(OH) 2. This method or precipitation maytherefore be used to make the more basic lead carbonate pigments theCaCO3 and-PbClz being added in successive batches in such a mannerasto-secure the most basic.compound possible. The

basic. lead-calcium-chloro-carbonate may; also be made from the solidlead chloride by mixing it with theprope'r proportion of finely dividedcalcium carbonateand treating the mixture with hot or preferably boiling-waterfand also prefer ably-grinding and agitating themixture aspreviously described; This basic compound. is not stable. and whentreated with hot or cold water slowly decomposes intoa mixture of basiccarbonate, 2PbCOsPb (OH).2- and PbCOI-Dz as in.-

dicated in the following chemical equation:

.zrbcnrmomecacop This decomposition is relatively very slow but can behastened byusing hot water and changing the water as the CaClz contentincreases ai idpare:

ticularly by grinding which removes the solid decomposition productswhich tend tocoat the original salt, If the basic chlorocarbonate'didnot decompose in the manner described itmight be; used as a paintpigment as it'is a white come the basic -lead-calcium chloro-carbonate.previously noted,*bytreating the basic lead-calpower; V The basiclead-calcium chloro-carbonate may be completely convertedto thenormalcarbonate by treatment with CO2 in an emulsion with water asindicated in the chemical equation given below: s

v V 2Pbc03+cac12+n2o This treatment is best carried out in an emulpoundwith 89% tintinsstrehg'th T sion of the basiclead-calcium-chlor'o-carbonate with'water or a dilute brine asconcentrated (and particularly hot concentrated) 'brines tend to'preventcomplete precipitation of. the lead as i r a carbonate. The CO2 drivenoff. during precipitation of thebasic lead-calciuin-chloro-carb'onatemay be used *fo'rthis conversion of the basic double salt to leadcarbonate and thus avoid the necessity of securing much of the CO2; fromother sources for this purpose. The conversion p to the carbonate isbest carriedout inia suitable spray chamber in which the fluidfpulp'mixture is sprayed into the'COz atmosphere.- mal carbonate thusproduced may beusedin the making of the basiolead'carbonate as describedbelow, I i 1 1 3 ..This basic lead-calcium-chloro-carbonate, made byprecipitation from the hotlsolutionsas described above, is used in myinvention forthe. l preparation ofv basic lead carbonate" 'or whitele'ad. This process may be carried out initw v general ways as follows:

The basic lead-calciunrsalti is mixed with PbClzand Ca'COa in theproportions to form the basic carbonateorwhite lead and the mixture isthoroughly ground for a period of from onehalf to two hours, andthenagitate'd with water The norwhich is changed at intervals as the021012 con centration increasesl This treatment results in theslowchange of the salts'in the mixture to basic lead carbonate and CaClZas'indicate'd in l the following chemical equationz" a2PbCQ3;Pb(OH)2+2CaCl2. forming-an excellent .white pigmentrof hightint-' ing strength and covering power. By varying the proportions ofthe basic lead-calcium salt and-the Pbclz and, CaCOsa whitelead of anydesiredbasicity may be secured, varying from the normal carbonate,formed by the reaction between the PbClz and CaCOz alone as describedthe firstpartof the specification, to the basic 'carbonateqjust'described; or an even more basic mixture mayabe formed by using anexcess of As cium-chloro-carbonate with water a. compound (or mixture)-more-basic than the ordinary basic lead carbonate (beingone molecule ofcarbonate,

to one molecule of hydroxide) The decomposition 'oflthe basicchloro-carbonate by wate'rv is slow in cold water but'if carried out inwater which is too hot, i. e.,near the boiling-point; there is achemical change which gives the pigment a light yellow color. The".reaction is also much hastened by-grinding during the treatment. The

whitelead pigment thus formed has a much higher tinting strength andhiding i power than the 'crdinarygba'sic lead carbonate, but care mustbe taken in drying not toheatmu'ch above Ci or else the pigment losesits white 0010a and turns a light'yellow. All of the compounds ormixturesofthis series are excellentwhitelpaint than with cold Water.

. reaction.

pigments, but the tinting strength and hiding power increase withtheincrease in ba'sicity from the normal carbonate to the fully basiccarbonate and is highest in the compounds (ormixtures) more basic thanthe basic carbonate zpboosrmomz.

To complete this process and remove practically the time necessary forcompletion of the reaction free from lchlorine.

and gives; a product of'higher tinting strength and hiding power.Complete removal of all the last: small amount of chlorine is notnecessary unless the product isto be used for making oxides chlorine inthe white pigments seems to increase their tinting strength andhidingpower, 7 To remove thelast of the chlorine'a period of several :daysgentle agitation or soaking in water ;is-'necessary. By this methodpractically all :the chlorine-may be renioved'(as CaClz) giving aproduct of the highest purity in this regard.

1 "After the ,removalof most .of-the chlorine (CaClz) by grinding andagitation, the residual chlorine is best removed by brief grindingperiods alternating withLlongperiods of agitation or soaking with.Water. After completion of the reaction the solutionmay be filtered--away from the compound and the latter may be dried or the requiredamount of linseed oil (or other oil) may be added to the wet'mixture'and incorporated therewith to form a whitel'lead paste in the well knownmanner now in common use.

The pigment; thus made, as it comes from the drier has a relatively highoil absorptionbut the oil absorption can be greatly reduced by a briefperiod' of grinding in a suitable mill such as a pebble mill, thedecrease in oil absorptionbeing roughly proportional toathe amount ofgrinding 1 to relatively low in. the thoroughly ground pigdetail of.operation.

orltime of grinding. By thus varying the grinding. time, white leadpigments, of different oil absorption may be made varying" fromrelatively high in the dried but unground pigment ment. V V e I 7 Itwill; be apparent that the process. may be carried out in a number ofdifferent ways as to For example, all the GaCOz required maybe addedtothe lead chloride solution 'in the'precipitation of the basic lead-calcium-chloro-carbonate and the required amount of PbClz may be added tothis mixture before grinding and treatment with water as described. Theprocess may ,also'be carried out by first preparing the normal leadcarbonate by either of the methodsdescribed above and theibasic;'leadcalcium chloro-carbonate as described and then mixing thesein thedesired proportions and grinding and treating with water as described.During this treatment the mixed salts react to form; thebasic. carbonateas indicated by the foli chloroecarbonate and lead carbonate white leadA y'ery small amount of mixtures of varying basicity maybe secured,varying in tintingstrength and covering-power as previously described.As previously noted grinding gives a. product of higher tinting strengthand hiding power. e e The basic lead carbonates or basic lead carbonatemixtures of varying basicitymay also be the basic carbonate as indicatedin the following chemical equation:

, ee co -rnoflebcoarmom z coz r This decomposition of the normalcarbonate,

prepared as described above, by treatment with boiling water, isrelatively slow requiring several hours for completion. In this regardit will be seen that the normal carbonate prepared by the methods hereindescribed diiiers entirely from the normal carbonate secured by ordinarymethods of precipitation. (Grinding during the treatment considerablyincreases the rapidity of the conversion. By boiling the normalcarbonate made as described, for different-periods, mixtures of varyingbasicity may be'secured varyingrfrom the normal carbonate PbCO3 to thefully. basic carbonate 2PbCOs.PbOI-I) 2. .These products also show theincrease in tinting strength .and hiding powerwith rincrease inrbasicitypreviously mentioned. Grinding" during the conversion gives a product ofincreased tinting strength and hid ing power.

The basic lead carbonate may also be formed directly from the leadchloroacalcium carbonate by treating it with hot or preferably boilingwater, or hotwater and'steam, thus driving QfiICOz and making calciumchloride and forming the basic lead carbonate as indicated in. thefollowing chemical equation;

srrbclzrbcoacaoog)+23 6 This operation is preferably carried out 'while'grinding during the treatment. j s a by mixing the lead chloride andcalcium carbonate in the proper proportions and grinding. in thepresence of hot or boilingwater or hot water and steam, thus driving ofi'COzand making calcium chloridein solution andforming the basio'leadcarbonatejas indicated equation:

in the following chemical The basic lead carbonate may also be prepared.

Changing the hot solution for fresh waterrat intervals during thetreatment is preferable as noted in the previousdescriptions.

The basic lead carbonate andbasic lead .car-

bonate mixtures may also be formed from the normal carbonate and leadhydroxide'or lead oxychloride as described in thefollowing. The normallead carbonate prepared :as described in the first part of thisspecification .is mixed with Pb(OH)2 in the proper proportion and theture is ground and treated with water'as previ-i ously described. Thistreatment of the mixture equation:

The basic compound thus'slowly formed isan excellent pigment,itsproperties being apparently Garbonate as indicated in the followingchemical due to themethod of formation in which it is veryeslowlyformed; By varying the proportions of hydroxide and carbonate whiteleads of. vary- ;ing basicityinayabe secured as previously described; I.

The foregoing-process preferably carried'out: by'mixing thepPbClz;CaCOaand Ca(OH) ain; the required (or desired) proportionsfand thengrinding the'lmixture and treating; with water as described, thismixture as a result of this treatment being slowly converted to thebasiclead carbonate as indicated by the following chemical'equation:

3PbCl2+2CaCOs+Ca(0H)z= 2PbCO3.Pb(OH) 2+3CaC12 By varying the proportionsof .CaCOa and Ca(OH)2 white lead mixtures of different basic ities maybe secured as described above. f

In the precipitation .of chloride solutions with calcium hydroxide,'oxychlorides or hydroxychlorides may be formed.v If theseare mixed withPbClz and CaCOs (or the PbCl2 and PbCOs preg pared as described) in theproper proportion and resultant product is the basic; lead carbonate.

ground and treated with water as described, the

The reaction occurring in the mixture is indicated in s the followingtypical chemical equations:

Any of the oxychloride compounds of lead may thus be converted to'thebasic carbonate by mixing with the proper proportions of Pbclz and CaCOsand grinding .the mixture and treating with water as described. Basiclead carbonate mixtures or compounds of varying basicity may be securedby varying the proportion of the differentingredients as previouslydescribed.

It will be apparent from the foregoing that other combinations of thedifferent steps of. making basicleadcarbonate or basic lead carbonatemixtures from lead chloride may be used, the

essential part of each method being that the mixture contain the'properproportions of lead and calcium compounds containing the properproportions of CO3 and (OH) z, for example, of

the, basic lead-calcium-chloro-carbcnate and PbClz and CaCO3, or basiclead calcium-chlorocarbonate and normal carbonate PbCOs, or PbClz andCa(OH) or Pb(OH) Cl and PbCIz and 09 003, etc., in the properproportion. Treating these mixtures by grinding and agitating with wateras described, preferably grinding the mixture with water and thereafteragitating with water as described, preferably grinding themixture withWater, and changing the water atjintervals, or

. grinding and agitating themixture with water and changing the water atintervals to remove the CaClz formed, gives the products described, Inall these methods grindingduring the conversion to the carbonate orbasiccarbonate increases the tinting strength and hiding power of the Thedifferent lead carbonate compoundsor mixtures mentionedin the foregoingmay also a hot concentrated and vpre'ferablyslightly acid chloridebrinapreferablyNaCl (crease if desired); Bydiluting and-cooling a;concentrated PbClz: solution made in thisway the PbClz-may beprecipitated and recovered. in the solid form and maybelused'for themanufactureof the leadcarbonates :by the'methods'previously described. FBy:=

diluting sucli'a concentrated chloride brineicon'a taining. PbClz'andtreating] with CaCOa as "described above th'ellead maybe precipitatedeither as the lead-calcium-chloro carbonate or as "the basicleadcalcium-chloro carbonate; as described' in the foregoing, which saltsmay be utilized for {the production ofthe difierent le'a'd carbonates aspreviously described. Inthe use of lead sulphate for these purposes itis necessary to take precautions to" prevent the precipitation ofPbelzrmonmcacoa, since the CaSOi Wiu react with the PbClz in these saltsin contactwith water or-dilutejbrines to formrPbSOi as indicated in thefollowing chemical equations f g a PbClz+CaSO =l=bSO4+CaCl q.

This reaction" does not occur in a concentrated brine but does occurinwater or dilutenbrines. The effect of brine-concentration onthereaction I is shown in curves III and IV. The coordinates of thesecurvesare percent NaCl in the brine and percentage of the total leadPbprecipitated from a PbClzsolution as PbSOior converted to PbSO4 byaddition of a small excess of CaSO4; III is l 'for a clean NaCl brine.IV is for a NaCl brine i containing one-half of one percent ofHCl; As

will-be noted from curve III, there is n0 precipitation Of PbSO4 by02504 in solutions containing. 7 above 10% NaCl, whereas below this;concentration the percentage of the lead in solution which isprecipitated or held out of solution as PbSOrby thejCasOr increasesalmost'directly as the brine concentration decreasesuntil'in a watersolution the lead chloride is all converted toPbSOi; As shown in curveIV, the addition of a small amount of HCl lowers the brine concentrationnecessary to prevent the reaction between the PbClz and CaSOr toapproximately eight percent NaCL Addition of more HCl still fartherlowersthis'required, brine'concentration. Where CaSOr is present or maybe formed, brines should therefore not be diluted below thesepoints. (8or 10% NaCl)I in the manufacture of PbC12' vfrom PbSO i; if a pure PbClproduct is desired.

From the curves I and III, it will be apparent that toprecipitate a purebasic lead -calciumchloro-carbonate from a brinejcontaining C3504 insolution, the brine should not be diluted below 10% NaCl to preventcontamination with PbSO4,

andthat the concentration of NaCl should not be much higher than12 inorder to secure substantially complete precipitation 'of the 'PbClz asthe basic lead-calcium-chloro-carbonate.

. Precautions must also be taken in the leaching of lead-ores with NaClbrines containing CaClz 70 V solution to prevent precipitation of CaSO4with, J g r the PbClz' in the cooling and dilutionlof the pregnantsolution, since in the later treatment will react with;

to which H2804 is added'to formthe leaching of the PbClz with water theCaSO; the PbClz to form PbSO4.

6 p 1,992,191 r V a V 3.-The process of makingbasiclead carbonate. fromlead chloride which consists in making 1ead 1 Having. described myprocess-what I claimand V desireto patent-is: l V

g l; Theprocess .of making. lead carbonate from. lead chloride whichconsists in making leadcalcium-chloro-carbonate by treating leadchloride with caloium carbonateand water. and washing out the calciumchloride formed in said treatment and thereafter treating saidchloro-carbonate with' water and thereby makingcalcium chloride insolution and forming, lead carbonate.

' 1 2. :The'proce'ss of making lead carbonate. from f lead "in achloride solution which consists in precipitatingthe leadas alead-calcium-chlorocarbonate, by means of calcium carbonate andseparatingsaid precipitate from'the solution and thereafter treatingsaidr-chloro-carbonate with water and thereby making calcium chlorideinsolution and torming lead carbonate.

calcium-.chloro-carbonate by treating lead chloride with calciumcarbonate'and water and thereafter treating said chloro-carbonate withhot; water and thereby making calcium chloride solutionand forming basiclead carbonate.

4.; 'Iheprocessf of making basic lead carbonate from lead chlorideinsolution. which consistsin precipitating the lead as alead-calcium-chloro carbonatewith calcium carbonate and se'parat-f ingsaid: precipitate from the solution and treat ing said precipitatedchloroecarbonatelwith hot water and thereby making" calcium chloride insolution and forming basic lead. carbonate;

' N IELso. cHaisTENsENf

